The present invention relates to a multiple outlet valve and in particular, a valve having a very low flow resistance therethrough, especially such a valve in conjunction with pressure relief systems.
In the chemical industry, overpressure relief systems are a requirement of almost every pressurized line, tank or other vessel. The most common types of relief devices are rupture discs and relief valves. Rupture discs present an inherent problem in that once they rupture, the disc must be replaced in order for the relief device to occlude the vent line associated therewith. Therefore, the ruptured disc must be removed and replaced with a new disc. Where the material in the line or tank is toxic or otherwise hazardous, the line or tank must often be completely emptied and purged before the rupture disc may be replaced. In addition, if the material in the line or tank is volatile in nature, a substantial amount of the material may escape into the vent system before the rupture disc can be replaced.
Relief valves somewhat overcome the problem associated with ruptures discs in that valves are biased to close and thereby occlude the vent line after the pressure in the system returns to an acceptable level. However, relief valves are relatively expensive compared to rupture discs. In addition, relief valves require a great deal of maintenance in order to insure their workability and therefore must frequently be removed from the process and tested. Such removal again requires that volatile or hazardous materials be removed from process tanks and lines protected by the relief valve before the valve can be removed.
It is therefore desirable that multiple relief devices may be provided for a common vent such that the vent may be normally in flow communication with a first of such devices and, should the first device need repair and/or maintenance, be able to switch to a second device while isolating the first such device from the system. In switching from one relief device to another it is extremely important to ensure that the process under pressure is at all times protected by at least one of the relief devices. Therefore, according to the present invention, a valving mechanism is provided for use with multiple relief devices to insure that the pressurized system to be protected is always in direct flow communication with at least one of the relief devices, while allowing a selected one of the relief devices to be isolated from the pressurized system to be repaired and/or maintained.
It is further desirable to have a valve of the type described which has a relatively small flow restriction associated therewith as pressurized fluid passes therethrough. A relatively low flow restriction allows inlet piping, outlet piping, and the valve itself to be of a smaller size than compared to valves having a larger flow restriction associated therewith. It is further desirable that the valve be easy to maintain and dismantle should maintenance be necessary thereupon.
In operation of a valve in conjunction with a rupturable relief device such as a rupture disc, it is also desired that the valve should communicate the pressurized fluid in the line or tank to the unruptured relief device as soon as the pressure within the process returns to a non-overpressure state and stabilizes. In this manner, excess material from the process is not lost through the ruptured relief device beyond what is necessary to return the process to a non-overpressure state. Therefore, an automated control system has been provided by the present invention to automatically actuate the valve to communicate the process with an unruptured relief device. The control mechanism can also be manually overridden or may operate to partially swing the valve to the unruptured relief device so as to continue to vent some of the material and thereby relieve pressure but not to vent more than is necessary to reduce the pressure to an acceptable level.
In a modified embodiment of the present invention, the valve mechanism may provide a simple device for switching an inlet flow to a plurality of individual outlet conduits. This is accomplished with a valve mechanism which is relatively low in flow restriction and yet simple to operate. A further modification of the valving mechanism provides for a simple mechanism for switching multiple pairs of interconnecting lines, such as what is commonly known as a four-way valve, with little flow restriction.